Epidemiology and etiology

The distribution of the various species of malaria is not well defined but P vivax is reported to be prevalent in the Indian subcontinent, Central America, North Africa, and the Middle East, whereas P falciparum is predominantly in Africa (including sub-Sa-haran Africa), both East and West Africa, Haiti, the Dominican Republic, the Amazon region of South America, Southeast Asia, and New Guinea.5,48, Most P ovale infections occur in Africa, while the distribution of P. malariae is worldwide. Most infections in the United States are reported in American travelers, recent immigrants,

or immigrants who have visited friends and family in an endemic area. ' Placental transmission and blood transfusions are also sources of malaria.

Within minutes after the bite of the Anopheles mosquito, the sporozoites invade hepatocytes in the liver and begin an asexual phase called schizonts (exoerythrocytic stage or schizogony). The patient may be asymptomatic during this period. After a lapse of between 5 and 15 days (depending on the species), schizonts rupture to release daughter cells (merozoites) into the blood, which then invade erythrocytes. In erythrocytes the merozoites undergo a number of sequential forms: a ring form, troph-ozoite, schizont, and merozoite, which then invade new erythrocytes. This asexual phase is about 48 hours for P falciparum, P. vivax, and P. ovale, and 72 hours for P malariae. Subsequently, the merozoites develop into gametocytes and undergo a sexual phase (sporogony) in the Anopheles mosquito. In the mosquito, the gameto-cytes undergo a number of stages: zygote, ookinete, and oocyst, and finally transform into sporozoites in the salivary glands where it is again able to infect the next host. Unlike P. falciparum and P. malariae, which only remain in the liver for about 3 weeks before invading erythrocytes, P. ovale and P. vivax can remain in the liver for extended periods in a latent stage (as hypnozoites); this can result in the recurrence of the infection after weeks or months. Primaquine therapy is necessary to eradicate this stage of the infection.

Patient Encounter 3, Part 1: Malaria

TW is a 27-year-old male who had returned from Bamako, Mali in West Africa, after visiting his college classmate who was in the Peace Corps. While there, he accompanied his friend on a river trip to visit a number of villages. He indicates that he took steps to minimize mosquito bites and had slept under a mosquito net. He was well since returning from Africa until the previous day, when he had a temperature as high as 39°C (102.2°F), with anorexia, headache, chills, sweats, myalgias, and ab dominal pain. He took a few doses of ibuprofen but his fever came back after a few hours and he now presents in the emergency department with chills, high fever (greater than 39.8°C) (greater than 103.6°F), headache, abdominal pain, nausea, stiffness of the neck, and back pain.

Are the symptoms in this patient consistent with malaria? What places this patient at risk for malaria?

What additional information do you need to develop a therapeutic plan for this patient?

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